Surface mount capacitor and method of making same

ABSTRACT

A surface mount capacitor ( 10 ) and method for making the same. A solid slug or pellet anode body ( 1 ) is encapsulated in a case ( 6 ) of insulating material. An anode and cathode termination pair ( 2, 3 ) are formed with surface mount mounting portions on one side of the case ( 6 ). An electrical connection ( 4 ) is made from the cathode termination ( 2 ) to a cathode on pellet ( 1 ) through the case ( 6 ). An electrical connection ( 7 ) is made between an anode associated with the pellet ( 1 ) and the anode termination ( 3 ) externally of the case ( 6 ). The external connection ( 7 ) allows improved volumetric efficiency by freeing up space in the case ( 6 ) for a bigger pellet ( 1 ). The method includes mass producing these capacitors ( 10 ) by mounting a plurality of pellets ( 1 ) on a lead frame ( 11 ) with pre-formed anode/cathode termination pairs ( 2, 3 ), at least substantially encapsulating the plurality of mounted pellets ( 1 ) and each pellet&#39;s associated anode and cathode, singulating the encapsulated pellets ( 1 ) to expose a portion of the pellet anode, and applying the electrical external conductive path ( 7 ) between pellet anode and anode termination ( 3 ).

INCORPORATION BY REFERENCE

The contents of U.S. Pat. No. 6,380,577, issued Apr. 30, 2002, and U.S.Pat. No. 6,238,444, issued May 29, 2001, are incorporated by referencein their entireties.

I. BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to surface mount capacitors and, inparticular, to surface mount capacitors having a capacitive elementsubstantially encapsulated in a body or case.

B. Problems in the Art

Demand has steadily increased for surface mount capacitors. They areuseful for numerous and widely-varying applications and functions. Forexample, they are useful for maintaining signal integrity and high speeddelivery of charge in electrical and electronic components or devices.They are also particularly useful in switching functions. They areuseful for bulk decoupling capabilities to smooth transient requirementsseen by a power source.

The types and configurations presently available are numerous. Most havesome type of capacitive element inside an enclosure or case. Externalconductive connections or terminations are electrically connected to theinternal capacitive element. The capacitor assembly can be placed upon acircuit board and connected to the circuit through the terminations.

Different capacitive element configurations produce different capacitiveperformance. The nature of the capacitive elements can determine theirsize. For example, some need to handle high voltage and, to do so, mustuse relatively large capacitive elements. This results in a relativelylarge case size.

However, many times the size of electrical components is important incircuit design. This brings what is called “volumetric efficiency” intoplay. Volumetric efficiency is known in the art to refer to capacitanceper unit volume. Two aspects of volumetric efficiency relative to thepresent invention are as follows.

First, there is volumetric efficiency of the capacitive element itself.Some materials have a higher capacitance performance than others for thesame size or volume. A good example is tantalum. It is well-known that asolid tantalum capacitive element exhibits more capacitive performancethan aluminum for the same volume.

Second, there is volumetric efficiency of the entire capacitor; namelythe capacitive element(s), case, and terminations. The case defines acertain volume. If the volume of the capacitive element inside the caseis small relative to the total volume of the case, the volumetricefficiency of the entire capacitor is normally lower than if the volumeof the capacitive element is large relative to case size.

If room on the circuit board for the capacitor is not a concern,volumetric efficiency may not be a concern. However, as can beappreciated, volumetric efficiency becomes increasingly important asspace for the capacitor becomes more limited. As increasingminiaturization occurs for a wide variety of electronic and electricaldevices, demand increases for increasingly smaller surface mountcapacitors.

Capacitors can represent the highest part count in many circuits.Therefore, a reduction in case size (and thus volume) of capacitors,while maintaining (or even increasing) capacitive performance, is animportant present need in the art. Circuit designers need to be able tospecify a certain case size for capacitors to allow them to fit on acircuit board with the other components needed for the electrical orelectronic device.

However, it is difficult to simultaneously meet increasing capacitiveperformance needs and at the same time have a very small package or casesize. Minimizing size while maintaining or improving capacitorperformance is a challenging task. Additionally, independent of casesize, there is always a need to improve the performance of, andvolumetric efficiency of, capacitive elements and capacitor assemblies.

One way to improve volumetric efficiency is to use a high performingmaterial, for example tantalum (Ta), Niobium (Nb), or Niobium Oxide(NbO), for the anode material. Solid core or pellet surface mountcapacitors of this general type are well known in the art. Examples canbe seen at U.S. Pat. Nos. 6,380,577 and 6,238,444, incorporated byreference herein. In those patents, the solid interior core (sometimescalled an anode body, slug or pellet) is primarily Ta. The tantalumanode body is usually sintered. A wire is commonly formed in the anodebody in one of two ways; (a) “embedded”, meaning the wire (also can beTantalum) is covered with Tantalum powder during a pressing process or(b) “welded” meaning after the pellet is pressed and sintered, the wireis welded to the Ta slug. The other end extends outside the slug. Thecapacitor dielectric material is made by anodic oxidation of the anodematerial to form an oxide layer over the surface of the anode body (e.g.Ta→Ta₂O₅). If the anode body is Nb the oxidation is Nb→Nb₂O₅; if NbO,the oxidation is NbO→Nb₂O₅. A capacitor cathode is commonly formed bycoating the dielectric layer with a solid electrolyte layer (e.g. ofMnO₂) and a conductive polymer, and later covered with graphite andsilver for better conductivity and improved mechanical strength. Anodeand cathode terminations can be connected to the free end of the Ta wireand the outer electrolyte surface coating of the Ta pellet,respectively, and all these components can then be encapsulated within acase (e.g. by molding plastic around the components), leaving only outersurface(s) of the anode and cathode terminations exposed on the exteriorof the case for, e.g., surface mounting.

U.S. Pat. Nos. 6,380,577 and 6,238,444, describe surface mount tantalumcapacitors of this general type. However, the terminations extend aroundthe edges of the case ends in a U-shape. Therefore, they are known as“wrap around” terminations. As can be seen at FIG. 6 of U.S. Pat. Nos.6,380,577 and 6,238,444, these “wrap around” portions (reference number36) provide an anode/cathode termination pair in two planes or sides ofthe device. While this allows the device to be surface-mounted on one oftwo sides (they can be referred to as “two-sided terminations”), ascompared to “single-sided” terminations, which can be surface mounted onone side only, it presents a problem. These “wrap around” or “two-sided”terminations can result in shorting between opposite ends of the devicewhen in place on a circuit board. An example of this shorting problemexists in many radio frequency (RF) applications where metal shieldingis placed over at least portions of the circuit boards. Portions of theconductive terminations extend up to and into the top plane of thecapacitor case.

Therefore, there is a demand for capacitors with “single-sidedterminations”, meaning an anode and cathode termination pair for surfacemounting exist on only one side or plane of the device. Oneconfiguration for such capacitors is illustrated in the drawing of FIG.13A, a solid slug (e.g. Ta) capacitor. This cross-sectional view shows aconventional tantalum slug or pellet 1 with an outward extendingembedded tantalum wire 9 encapsulated in case 6 of plastic material.Anode termination 3 is positioned on what will be called the bottomsurface of encapsulating material or case 6 directly underneath the freeend of wire 9. A conductive adhesive 4 and an internal conductive path15 electrically communicate the free end of wire 9 with anodetermination 3 through the encapsulating material 6. A cathodetermination 2 (also on the bottom side of the encapsulating material orcase 6 but directly underneath the end of pellet 1 opposite wire 9) iselectrically connected to the exterior of pellet 1 through another padof conductive adhesive 4. Thus, in comparison to the wrap aroundterminations of the capacitors of U.S. Pat. Nos. 6,380,577 and6,238,444, the capacitor of FIG. 13A has single-sided terminations. Theanode and cathode terminations are in the same general plane on oneside, the bottom side as shown in FIG. 13A, of the capacitor device. Asimilar prior art embodiment of such a single-sided terminationcapacitor is illustrated in FIG. 13B.

While the prior art capacitors of FIGS. 13A and B do not present theearlier discussed problem associated with the “wrap around” terminationsof U.S. Pat. Nos. 6,380,577 and 6,238,444, they do present a volumetricefficiency issue. As shown in the cross section views of in FIGS. 13Aand B, the encapsulating material of case 6 encases not only pellet 1but all of the outward extending portion of wire 9. In particular, thereis a substantial volume of case 6 between the distal end of wire 9 andthe outer surface of case 6. Sufficient space must be allowed for theinterior electrical connection or path 15 between wire 9 and anodetermination 3. In essence, a rather substantial volume of encapsulatingmaterial in case 6 is used up to completely encase both the free end ofwire 9 and the connection 15 between wire 9 and anode termination 3.This limits the size of Ta pellet that can be placed in case 6. Asubstantial volume of the entire capacitor case must be dedicated to theelectrical connection of wire 9 to anode termination 3, as opposed tobeing filled more completely with pellet 1.

Therefore, a need in the art exists for a surface mount capacitor withimproved volumetric efficiency.

Furthermore, it is difficult to optimize volumetric efficiency(capacitance per unit volume of the device) when manufacturing suchcapacitors, especially when the devices are of the smaller case sizes.It is difficult to control the thickness and uniformity of thickness ofthe encapsulating material around the capacitive element (e.g. pellet1), both when molding the material around the pellet and when producingthe final device. This is either ignored or tends to result inover-compensation in designs and manufacturing steps that result inthicker case walls which, in turn, limits space for the capacitiveelement. Many present state-of-the-art capacitors therefore haverelatively thick case walls. Volumetric efficiency suffers.

As can be appreciated, these volumetric efficiency issues apply to othersingle-side termination surface mount capacitors as well. Any increasein volumetric efficiency can potentially be beneficial regardless ofsize or type of capacitor. A real need in the art has therefore beenidentified for an improved single-sided termination surface mountcapacitor.

II. SUMMARY OF THE INVENTION

It is therefore a principal object, feature, aspect, or advantage of thepresent invention to provide an apparatus and method which improves uponthe state of the art.

Other objects, features, aspects, or advantages of the invention includean apparatus or method which:

a. improves volume utilization or volumetric efficiency;

b. improves flexibility for molded case surface mount capacitors,including the ability to produce a variety of sizes with the sameassembly line and molding equipment;

c. is efficient and economical, including for small case size massproduction;

d. can be implemented in large scale manufacturing techniques;

e. reduces risk of shorting between terminations as compared to wraparound terminations.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent with reference to theaccompanying specification and claims.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective diagram of a capacitor according to one aspectof the present invention.

FIG. 1A is similar to FIG. 1 but has different terminations.

FIG. 2 is a perspective view of the capacitor of FIG. 1 but inverted toshow its bottom surface and termination configurations on the ends ofthe case of the capacitor.

FIG. 2A is similar to FIG. 2 but with the alternative terminations ofFIG. 1A.

FIG. 3 is a sectional view taken along line 3—3 of FIG. 1, slightlyenlarged from that of FIG. 1.

FIG. 3A is similar to FIG. 3 but with the alternative terminations ofFIG. 1A.

FIG. 4 is a slightly enlarged bottom plan view of FIG. 1.

FIG. 4A is similar to FIG. 4, but with the alternative terminations ofFIG. 1A.

FIG. 5 is a diagrammatic side elevation, partial sectional depiction ofa plurality of tantalum pellet/wire (could be embedded or welded)combinations mounted on a metal substrate or under layer, also called alead frame, to illustrate one step of an exemplary manufacturing methodfor capacitors of the type of FIG. 1 according to one aspect of thepresent invention.

FIG. 6 is a top plan view of FIG. 5.

FIG. 7 is a reduced-in-size top plan view of a subsequent molding step,showing a plurality of combinations like shown in FIGS. 5 and 6 but withan encapsulating material applied to them (part of the encapsulatingmaterial is shown cut away for illustration purposes).

FIG. 8 is a slightly enlarged perspective view of a portion of FIG. 7.

FIG. 9 is a perspective illustration of a subsequent singulation stepfor producing a plurality of partially completed capacitors from themolded array of FIG. 7.

FIG. 10 illustrates, in isolation, an enlarged view of one of thepartially completed capacitors of FIG. 9 but from a bottom perspective.

FIG. 11 is similar to FIG. 10 but shows a subsequent metal deposition orsputtering manufacturing step—adding an external conductive path at oneend of the partially formed capacitor. This could also be done at bothends.

FIG. 11A is similar to FIG. 11 but with the alternative terminations ofFIG. 1A.

FIG. 12 is similar to FIG. 11 but illustrates a final manufacturing stepfor the capacitor—plating the external conductive path and the twobottom terminations.

FIG. 12A is similar to FIG. 12 but with the alternative terminations ofFIG. 1A.

FIG. 13A is a cross-sectional view similar to FIG. 3 but illustrating aprior art capacitor of the general tantalum pellet surface mount type,showing a internal electrical connection between the interior tantalumpellet and the external bottom anode termination for a particular caseor package size capacitor.

FIG. 13B is similar to FIG. 13A but with the alternative terminations ofFIG. 1A.

FIG. 14, for comparison, is a similar cross-section to that of FIG. 13Afor the same case or package size for an exemplary embodiment of thepresent invention and shows how it improves volumetric efficiency forsuch a capacitor.

FIG. 15 is a perspective view of a finished capacitor according to oneexemplary embodiment of the present invention but shows the case inghost lines and the other components in solid lines.

FIG. 16 is a sectional view of another prior art device.

FIG. 17 is a reduced-in-scale top plan view of a lead frame assemblywith a plurality of capacitors mounted thereon.

IV. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT ACCORDING TO THEINVENTION

A. Overview

For a better understanding of the present invention, an exemplaryembodiment will now be described in detail. Frequent reference will betaken to the above-described drawings. Reference numerals and/or letterswill be used to indicate certain parts or locations in the drawings. Thesame reference numerals and/or letters will be used to indicate the sameparts or locations throughout the drawings unless otherwise indicated.

The context of this exemplary embodiment is a surface mount capacitor ofthe general type disclosed in U.S. Pat. Nos. 6,380,577 and 6,238,444except rather than “wrap around” terminations, it has single-sidedterminations-anode and cathode terminations are both in generally thesame plane on only one side (here the bottom surface mount side) of thedevice. In particular, this exemplary embodiment is a surface mountmolded solid electrolyte tantalum capacitor having anode and cathodeterminations on the bottom plane of the casing. The casing size of thisexample, case size 0603 (such as is known in the art), is relativelysmall (approximate dimensions: length of 1.6 (+/−0.1) mm; width of 0.8(+/−0.1) mm; and height of 0.8 (+/−0.1) mm). This represents a casevolume of roughly a little over 1 mm³. Examples of other relativelysmall case sizes are 0402 and 0805. However, the invention is notlimited to any particular case size or any particular material orconfiguration of capacitive element inside the case. In fact, theinvention can be scaled up or down as desired. One of the advantages orfeatures of the invention is that ability—namely, the ability to applythis to a variety of different capacitor package sizes while using thesame concepts and manufacturing techniques.

B. Exemplary Apparatus

By reference to FIGS. 1–3, 14, and 15, an exemplary capacitor 10,according to one aspect of the present invention, is illustrated.Capacitor 10 includes an outer case or encapsulating material 6 ofconventional plastic material. The case size of case 6 is 0603. Anexternal anode polarity marking 8, conventional in the art, provides avisual indication on the top surface of capacitor 10 of its anodetermination end (see FIG. 1).

Capacitor 10 is elongated along a longitudinal axis (see broken sectionline of FIG. 1). Its bottom surface (see FIGS. 2, 3, 14, and 15)includes anode termination 3 and a cathode termination 2. They areconventional and made of conventional material (e.g. copper (Cu) orsilver (Ag) or nickel alloys). Terminations 2 and 3 are at opposite endsof, and their facing edges are separated an acceptable distance fromeach other, on the bottom of case 6.

By referring to FIG. 3, inside case 6 of capacitor 10 is a tantalumanode body, pellet or slug 1. It could be made of other analogousmaterials (e.g. Nb or NbO). It is pre-manufactured according to knownmethods, as previously described. It is also elongated along thelongitudinal axis of capacitor 10 but has a layer of encapsulatingmaterial 6 around most of it to isolate and insulate it from theexterior. As is conventional, a tantalum wire 9 is connected to pellet 1and extends out one end of pellet 1 inside case 6.

The foregoing components are generally conventional in the art. Tobetter understand differences of capacitor 10 from state of the artsingle-sided termination surface mount tantalum slug capacitors,reference will now be taken to FIGS. 13A, 13B and 14.

FIG. 13A shows the conventional state of the art or prior art structurefor these types of capacitors. FIG. 13B shows a similar prior artvariation. Such capacitors encapsulate all of wire 9 in the case,leaving a substantial amount of volume of the case surrounding all sidesof wire 9 and slug 1. Internally (or substantially internally), there isan electrical conductive path 15 between the encapsulated end of wire 9and the external anode termination 3, and an electrical path 4 betweenthe slug surface at the opposite end of pellet 1 and cathode termination2. Therefore, the only electrically conductive external components onthe prior art capacitor of FIG. 13A would be the outer surfaces of anodeand cathode terminations 3 and 2 on the bottom of the capacitor and theexposed end of wire 9 in the plane of the end of the capacitor. All elseis encapsulated in case 6. FIG. 13B is likewise except a part ofconductive path 15 is also exposed along the wire 9 side of the case.

In comparison, with particular reference to FIG. 14, as well as FIGS.1–4 and 15, capacitor 10, an exemplary embodiment of the presentinvention, differs from that of the prior art capacitors of FIGS. 13Aand 13B primarily in the following ways.

First, the length Lp+20%, of Ta pellet 1 of capacitor 10 of FIG. 14 issubstantially longer than, and therefore substantially larger in volumethan, the length Lp and volume of the Ta pellet of the capacitor ofFIGS. 13A and B (see indication in FIG. 14 that in this particularcomparison, length of the Ta pellet of capacitor 10 is approximately 20%longer).

Second, wire 9 extends to the external boundary of one end of case 6. Itis intentionally exposed (see FIG. 10). An external conductive path 7(e.g. a metal deposition layer) is added (e.g. by conventional metaldeposition techniques). All individual units undergo deposition of aconductive layer that covers one or both capacitor ends in a processsuch as sputtering, stencil printing, or screen printing. The materialsused for such a process could be metals such as: Ag, Ni, Cr, Ta, Cu, Au,Pd; or alloys such as: AuPd, NiCr, NiPd or polymer based pastescontaining such metals. This conductive layer allows reliable electricalcontact between the anode wire and the metal array which is used asanode termination of the capacitor. Refer to FIGS. 1–4, 10–12, and 15 tosee how external conductive path 7 connects wire 9 and anode termination3.

Third, in the prior art capacitors of FIGS. 13A and B, pellet 1 isusually directly electrically connected through the material of case 6to cathode termination 2, and wire 9 is similarly connected to anodetermination 3. Some type of electrically conductive material or member 4and/or 15 is usually between anode termination 3 and wire 9 and betweencathode termination 2 and the opposite end of pellet 1 respectively. Oneexample is an electrically conductive (e.g. silver based) adhesive (seereference number 4 in FIGS. 13A and B) that both binds pellet 1/wire 9to the terminations 2 and 3 during fabrication and provides anelectrically conductive path for operation of the device as a capacitor.Such conductive adhesive is well-known in the art and available from avariety of commercial sources. In comparison, in capacitor 10 the onlyelectrical path from wire 9 to anode termination 3 is through theexternal conductive path or member 7. Instead of an electricallyconductive adhesive or path between anode termination 3 and wire 9, aninsulator is used (here insulative adhesive 5) to support one end ofpellet 1 during molding, as will be described later. Such insulativeadhesive is well-known in the art and available from a variety ofcommercial sources. Capacitor 10 eliminates the need of room inside case6 for the internal conductive path 15 of FIGS. 13A and B. Electricallyconductive adhesive 4 is still used between pellet 1 and cathodetermination 2 (e.g. Cu) in capacitor 10. Furthermore, as indicated atFIG. 15, an addition insulative layer 14 can be placed between anodetermination 3 and pellet 1. Layer 14 can be made of dispensable andprintable surface mount paint/ink, such as “Perma CI Series Ink”available from Automated Industrial Systems, Inc. (Erie, Pa., USA), andcan have properties to adhere it to anode termination 3, oralternatively be adhered by appropriate adhesive.

Thus, FIGS. 13A and 14 illustrate one way capacitor 10 can increasevolumetric efficiency relative to the state of art capacitors. Forreference purposes FIG. 13A has the following dimensions indicated:L_(c)=length of case; L_(p)=length of pellet; L_(e)=length of externalconductive path, relative to the longitudinal axis of capacitor. Assumeeach capacitor of FIGS. 13A and 14 has the same case size (0603) andtherefore the same overall case height H_(c), case width W_(c), andlength case L_(c). Those dimensions would be equal for both FIGS. 13Aand 14. However, connection of anode termination 3 on the outside ofcase 6, with external electrical conductive path 7 between the exposedend of wire 9 and the anode termination 3, allows pellet 1 of capacitor10 of FIG. 14 to occupy more space inside case 6. Because the case sizeis fixed, this allows the volume of pellet 1 of FIG. 14 to be increasedrelative to the total volume of case 6. In other words, the length ofpellet 1 of capacitor 10 of FIG. 14 is substantially greater (20%) thanL_(p) of the tantalum pellet in the capacitor of FIG. 13A. Normally,capacitance of tantalum increases with volume. Therefore, by increasingthe volume of tantalum pellet 1 in comparison to the total volume ofcase 6, increased utilization of the case or package 6 is achieved (morecapacitance per unit volume) and, thus, improved volumetric efficiencyis achieved over that of FIG. 13A.

As indicated in FIG. 14, on the order of 20% increase in length ofpellet 1 is possible in this 0603 case by using external conductive path7 (e.g. pellet length can be increased around 1.00 mm to 1.25 mm). Thiswould therefore increase the volume of pellet 1 (although by somethingless than 20% because height and width remain the same). While theincrease in volumetric efficiency can vary depending on several factors,this could represent a substantial increase. Tests have indicated fromup to on the order of 70% increase in volumetric efficiency is possibledepending, in part, on case size. Testing indicates even greaterincreases might be possible (for example 100% or double or more).

C. Method of Manufacturing

By reference to FIGS. 5–12, an exemplary method of making capacitors 10is illustrated. The method can be used to mass produce capacitors 10.

1. Starting Materials

A plurality of pellets 1 are first produced by conventional methods.Each pellet is connected to a portion of wire 9. The portion outsidepellet 1 is cut to the approximate length shown in the Figures.

An electrically conductive (metal plate) substrate or lead frame 11 ispre-manufactured to include rows and columns of pre-formed adjacentanode termination 3 and cathode 2 termination pairs with open spacesubstantially around them (see FIG. 8).

2. Anode Terminal Insulation

A small electrically insulating pad 14 (shown only in FIG. 15) can beplaced on or adhered to the top of each anode termination 3 on leadframe 11. It covers most of the inner surface of anode termination 3.Unlike the anode termination of state of the art capacitors (see FIG.13A), which supports the pellet during molding of the case but alsosupports and electrically connects the anode termination with the pelletby the internal conductive path 15, here the anode termination merelysupports the pellet during molding but does not utilize that supportstructure or material (e.g. insulating adhesive) for an electricalconnection. Note how the longer pellet 1 in capacitor 10 extends moredirectly over anode termination 3. A substantial part of it is thereforein relatively close proximity to anode termination 3. Therefore,insulating pad 14 helps provide good electrical insulation betweenpellet 1 and anode termination 3.

3. Pellet to Lead Frame Assembly

Pads or dabs of electrically conductive adhesive 4 are then placed oneach cathode termination 2 of lead frame 11, and pads or dabs ofelectrically insulating adhesive 5 are placed on top of each insulatinglayer 14 on each anode termination 3 (see FIGS. 5 and 6). Individualtantalum pellet/wire combinations 1/9 are then placed or pressed downonto pads 4 and 5 to adhesively connect them to and support them on leadframe 11; one pellet/wire combination 1/9 to each anode/cathodetermination pair 3/2 by placing each pellet 1 in the orientation shownin FIGS. 5 and 6 (wires 9 pointing in the same direction). The end ofpellet 1 with wire 9 is on the dab or spot of insulative adhesive 5 onanode termination 3 (covers less area than insulative pad 14) and theother end of pellet 1 on conductive adhesive 4 on cathode termination 2.Note how the distal end of each wire 9 extends to generally the samevertical plane as the distal edge of its corresponding anode termination3.

Further steps of this method will be described by referring toindividual pellets or capacitors by position on lead frame 11. Byreferring to FIGS. 7–9, it can be seen that lead frame 11 can haveplural rows and columns of pre-formed anode/cathode termination pairs.For purposes of this discussion, columns on the lead frame are referredto by the letters A, B, C, D, E, etc., as indicated in FIG. 7. Rows areindicated by numbers 1, 2, 3, 4, 5, 6, 7, 8, etc. (see numbers alongother side of the lead frame array in FIG. 7). Individual pellets 1 willbe referred to by the reference numeral “1” followed by column and rowposition. For example, the pellet 1 in the first column and first row oflead frame 11 will be referred to by the reference numeral 1A1, thepellet in column B, row 1 by the reference numeral 1B1, and so on.

FIGS. 5 and 6 illustrate the step of adding pellets to lead frame 11,showing pellets A1, 1A2, 1B1, and 1B2 in place on their respectiveadhesive pads 4 and 5. Pellets have not yet been placed onto thepre-applied adhesive pads 5 and 4 in lead frame positions C1 and C2.Note how free space 12 exists in lead frame 11 between the facing edgesof each termination pair 3/2 for each pellet 1, and free space 13 existsin lead frame 11 between adjacent pellets 1. Referring also to FIGS. 7and 8, there is free space around most of the perimeter of the anode andcathode terminations in lead frame 11. This allows plastic to be moldedinto those spaces.

4. Molding

Once the desired number of pellet/wire combinations 1/9 are placed on,adhered to, and supported by their adhesive pads for each terminationpair (anode and cathode terminations) in the lead frame array 11(usually filling up all positions on the array), with wires 9 aligned inthe same direction for each pellet 1, encapsulating material 6 isapplied 2 over the array (see FIGS. 7 and 8). Part of the encapsulatingmaterial 6 is cut away in FIGS. 7 and 8 to show pellet/wire 1/9combinations in position in the array of columns and rows on lead frame11. Conventional, known-in-the-art machines and methods can be used tomold the encapsulating material around each pellet. It is usually aplastic that is applied in a liquid or semi-solid phase over lead frame11. As indicated previously, the pre-formed spaces around anode andcathode terminations in lead frame 11 allow the encapsulating materialto flow around and into spaces 12 and 13 to essentially encapsulatepellets and embedded wires, as well as partially underneath the pellets.The encapsulating material also flows and hardens around the perimeteredges of the anode and cathode terminations, except of course, for theportions of their perimeter edges that are integral with the remainderof lead frame 11 (these will be separated from the lead frame duringsingulation).

The encapsulating material subsequently hardens into a solid phase layerover frame 11 essentially encapsulating the pellet/wire 1/9 combinationson lead frame 11. A variety of ways to mold the encapsulating materialexists. One state-of-the-art method uses a commercially availablemachine. A tray holds the lead frame 11 (see also FIG. 17) and theadhered pellet/wire combinations in their generally evenly spaced apartpositions on lead frame 11. The tray is inserted into the machine whichapplies or molds the plastic over the lead frame.

5. Marking

As is conventional, an anode polarity marking can be laser-applied,stamped, molded, or otherwise applied to the top of each capacitor 10.FIG. 1 shows diagrammatically the position of such a marking 8. Themarking can be positioned at the anode end of the capacitor to visuallyinform a viewer of its location. It could include indicia, includingwords or symbols that specify, for example, a polarity bar and voltagecode, such as are known in the art.

Because the position of each pellet is relatively precisely known in thearray, the marking 8 could be applied to the top of the layer ofencapsulating material for each column and row location during or rightafter molding by automated means.

6. Dicing/Singulation

Following standard automated or semi-automated fabrication techniquesknown in the art, dicing or singulation then occurs. Cutting occursalong predetermined separation lines to singulate each pellet/wirecombination 1/9 from the continuous molded plastic layer (see, e.g.,FIG. 7). Cutting parallel to the longitudinal axis of each of pellet 1inbetween rows 1, 2, 3, etc., removes molded plastic from betweenadjacent sides of the pellets and creates generally planar vertical sidewalls. Cutting perpendicular to the longitudinal axis of each pelletbetween columns A, B, C, etc., removes molded plastic from betweenadjacent ends of the pellets creates generally planar vertical endwalls. It is controlled to leave the distal end of wires 9 exposed (seeFIGS. 9 and 10). The tops of cases 6 are also generally horizontallyplanar.

Also, the dicing or singulation step frees the anode and cathodetermination pair 3/2 for each pellet 1 from lead frame 11, and thebottoms are generally horizontally planar with the bottom surfaces ofthe anode and cathode terminations exposed. This can be accomplishedutilizing known in the art techniques and equipment so that eachencapsulated pellet 1 can be singulated into the form shown in FIG. 9.

A commercially available machine would receive the lead frame withencapsulated array of pellets. With proper alignment and positioning, itwould cut along the separation lines (several are illustrated in FIG.7). Unneeded plastic material would be removed from between each arraylocation. The separation steps produce a desired package or case sizefor each capacitor. They also expose the end of each wire 9. They canalso expose the outer edges of anode termination 3 and cathodetermination 2 at opposite ends of each case 6. Particularly note, inthis process, the edge of anode termination 3 is exposed in or near thesame vertical plane as the exposed end of wire 9.

As indicated in FIG. 9, the cutting steps result in the plurality ofrows and columns of encapsulated pellets/wires, and corresponding wireand anode/cathode terminations sets, being separated from lead frame 11,as well as producing the basic form of case 6 and terminations 2 and 3.This singulated array is then ready for finishing steps to make completecapacitors 10.

7. Application of External Conductive Path

Also by methods and machines well-known in the art and commerciallyavailable, external conductive path 7 can then be applied to eachsingulated combination of FIG. 9. One technique is metal deposition. Acontrolled-in-size, relatively thin, metal layer would be deposited onand adhered to the anode termination end (and possibly also the cathodetermination end) of each singulated encapsulated combination.

The path 7 would extend from completely covering the exposed end of wire9 down to covering the exposed edge of anode termination 3 (see, e.g.,FIGS. 3, 10, 11, 14, and 15). It can be a relatively thin layer (e.g. inthe range of 10 Angstrom to 10 μm, preferably 0.01 μm–10 μm and morepreferably 0.1 μm–5 μm thick), but sufficient to made a reliableelectrical contact between wire 9 and the metal array which is used asthe anode termination of the capacitor. In this embodiment, layer 7 doesnot extend to the top of case 6.

8. Plating

In this exemplary embodiment, a conventional plating process is used toapply an electrically conductive plating (e.g. nickel, thickness 0.5μm–20 μm, preferably 0.5 μm–3 μm, following by Pd or NiPd or Au or Sn orother standard metal plating in the thickness of 0.001 μm–10 μm,preferably 0.1 μm–5 μm) to the outer surface of each of externalconductive path 7, anode termination 3, and cathode termination 2 (seeFIG. 12). This introduces some additional, but relatively small,thickness to those parts (see thickness X_(E) in FIG. 14). Thiscompletes each capacitor 10. Thus, consecutive plating operationsproduce single-sided termination capacitors in relatively uniform casesize.

The completed, singulated capacitor 10 has an anode termination width Cand length P (see FIG. 2). The cathode termination has a similar width Cand length P. A distance P₁ exists between adjacent edges ofterminations 2 and 3 (see FIG. 2).

9. Testing and Packing

As is conventional, once the manufacturing steps outlined above arecompleted, capacitors 10 are tested for quality control and operation.Those passing inspection are packaged for shipment to an end user.

Thus, on a mass production scale, a plurality of individual capacitors10 can be manufactured using conventional fabrication techniques.However, placing the electrical connection between wire 9 and anodetermination 3 along the outside of case 6 frees up space inside case 6to increase the size of pellet 1. Without changing case size, morecapacitance capability is introduced. Thus, volumetric efficiency isincreased.

It can therefore be seen how the exemplary embodiment achieves thestated objects, features, aspects, or advantages of the presentinvention. Capacitors 10 can be manufactured with well-known, developedtechniques and machines. The manufacturing steps can be efficient incost and resources. They can be easily implemented for a variety of casesizes.

D. Options and Alternatives

It will be appreciated that the foregoing exemplary embodiment andexemplary manufacturing method are but one way the invention can bepracticed. They are presented for illustrative purposes only and not byway of limitation. Variations obvious to those skilled in the art areincluded with the invention.

For example, the invention is applicable to a variety of package or casesizes. It can be scaled up or down according to need. Package size of0603 has been described above. However, feasibility of the process andproduct has not only been demonstrated by producing capacitors in 0603(M case) size, but it is believed applicable to a wide range of, andpossibly any, case size. It could potentially be extended to Low Profilecase sizes. Some additional exemplary case sizes are 0402, 0603, 0805,and bigger sizes.

Capacitor 10 can be manufactured to at least standard tolerances in avariety of capacitance and other ratings, including relatively highpower applications. It could be utilized for low profile conformalsurface mount applications with high volumetric efficiency for energystorage, filtering, and by-pass. It could be utilized in microprocessorbased systems. It can be advantageous for other higher frequency, singlesided termination applications. These are but a few applicationexamples.

The invention can be utilized for use with electrical or electronicdevices of almost any type. Consumer, medical, and communicationproducts are prime candidates for such capacitors. RF applications arealso candidates. Some examples in communication and consumer segmentsare cell phones, personal digital assistants, and hand-held gamingdevices. Medical field applications are also of high potential. Thefields of application is not limited.

The precise type of capacitor can also vary. In the exemplaryembodiment, capacitor 10 is a chip capacitor of the type having atantalum slug or pellet which is sintered, formed and impregnated withmanganese dioxide or conductive polymer. Wire 9 is tantalum wire. Theouter surface of each pellet is covered with a cured silver paste thatserves as a cathode electrode. However, other materials for thecapacitive component can be used. The invention is not limited totantalum pellets or slugs. Other materials, forms, and configurationsfor the capacitive component, as well as for the case 6 or other aspectsof the capacitor are possible. Some alternative materials have beenmentioned earlier.

The metal deposition process provides accurate placement of the externalconductive path 7, and reliable electrical contact between anode wire 9and metal under layer 11 (the metal array which is used as the anodetermination of the capacitor). When the metal deposition step iscompleted, the external conductive path 7 does not extend all the way tothe top plane of case 6 in the embodiment of FIGS. 1, 2, 3, 4, 10, 11,12, and 14. However, an alternative exemplary embodiment of theinvention is shown at FIGS. 1A, 2A, 3A, 4A, 11A, and 12A. They show aslightly different single-sided termination capacitor according to thepresent invention. Instead of just one L-shaped anode termination 3/7(as shown in FIG. 2), L-shaped terminations exist on both ends of thecapacitor (see in particular FIGS. 2A and 3A). Conductive surfaces covermost of the ends of the capacitor. These L-shaped terminations areuseful for providing elevated strength of the solder joint to theprinted circuit board (e.g. when a customer needs stronger adhesion ofthe capacitor to the board (PCB), by means of creating a large meniscuson both capacitor ends after Reflow soldering). However, sinceconductive parts of the termination do extend to or near the top planeof the capacitor, there is some risk of shorting between thoseterminations. Similar construction steps to those of the first describedexemplary embodiment can be utilized to make this alternativeembodiment, including the steps to increase volumetric efficiency insidethe capacitor. Other shapes of the terminations are possible.

Another example of a prior art capacitor is illustrated at FIG. 16.Anode termination 3 and cathode termination 2 are of differentconfiguration. They are both C-shaped in cross section, as opposed tothe flat cathode termination 2 of FIG. 3 or the L-shaped anodeterminations 3 of FIGS. 3A and L-shaped anode and cathode terminations 3and 2 of FIG. 3B. In FIG. 16 the top free ends of the C-shaped anode andcathode terminations conductively connect to the outside MnO₂ cathodelayer and the top oxidized anode layer of wire 9 respectively (e.g. byconductive adhesive or otherwise). The bottom free ends form the singlesided surface mount portions of anode and cathode terminations 3 and 2on the bottom side of the case. The intermediate section of the C-shapedanode and cathode terminations extend along an exterior part of the endwalls of the case.

FIG. 17 illustrates another example of a lead frame and how capacitorsof the type of capacitors 10 according to the invention can be massproduced efficiently.

Furthermore, other methods can be used to improve volumetric efficiencyfor single sided termination capacitors. For example, advanced packagingtechnology (APT) can be used to reduce the thickness of the package orcase walls to further increase capacitor volume utilization. Again, lesscase thickness frees up more space within a given case size for morepellet. Both array molding and segmenting operations could utilize highprecision techniques that allow achieving thinner walls of plasticencapsulation. This, alone (and without the external conductive path 7),can increase volumetric efficiency of the capacitor by freeing up spacefor additional volume of the capacitive element or pellet.

But utilization of the external conductive path 7 and theabove-discussed high precision manufacturing methods, can togetherresult in a cumulative improvement of volumetric efficiency. Testing hasgiven indications that improvements of on the order of 70%, or higher,improved volumetric efficiency may be possible for certain pelletmaterial, namely tantalum, and certain package sizes. For example, theremight be as much as 100% or more capacitance increase over molded chipdesigns (see FIG. 16) in D case size (based on 80KCV, 6V ratingdesigns).

The exemplary method of producing capacitors 10 allows production of avariety of a small size and low profile case sizes using the sameassembly line and same molding equipment. However, it is to beunderstood that creation of capacitors like capacitors 10 does notrequire the use of the manufacturing or fabrication techniques describedearlier with the exemplary embodiments. Alternative methods arepossible.

Each capacitor can be surface mounted according to known methodologies.The applicability of these capacitors extends to all uses of surfacemount capacitors. A primary benefit of capacitor 10 is the ability tohave either smaller size for the same or greater capacitance or have agreater amount of capacitance for a similar sized case. Volumetricefficiency increase provides a significant advantage for manyapplications.

1. A surface mount capacitor comprising: a) a capacitive elementincluding an anode and a cathode; b) an encapsulation material forming acase around the capacitive element except for an exposed portion of theanode; c) an electrically conductive planar substrate comprising anodeand/or cathode terminations having surface mounting portions on a singleexterior side of the case and to which the capacitive element ismounted; d) a conductive path between the exposed portion of the anodeand the anode termination comprising an external conductive connectionon an external surface of the case.
 2. The capacitor of claim 1 whereinthe external surface of the case is on a side of the case different fromthe single exterior side of the case.
 3. The capacitor of claim 1wherein the case includes a top side, a bottom side, a first sidebetween the top and bottom sides, a second side between the top andbottom sides, a first end side and a second end side, and whereinsurface mounting portions of the anode and cathode terminations are onthe bottom side and the external conductive connection is on at leastone of the first or second end sides.
 4. The capacitor of claim 1wherein the external conductive path comprises a multilayer structurewith the range of 10 to 20 μm thick.
 5. The capacitor of claim 4 whereinthe thin layer comprises a metal deposition layer.
 6. The capacitor ofclaim 4 wherein the multilayer structure is 0.01 μm to 10 μm thick. 7.The capacitor of claim 4 wherein the multilayer structure is 0.1 μm to 5μm thick.
 8. The capacitor of claim 1 wherein the external conductivepath and anode and cathode terminations are plated with an electricallyconductive plating material.
 9. The capacitor of claim 1 wherein thecathode termination is electrically connected to the cathode of thecapacitive element by an electrically conductive material.
 10. Thecapacitor of claim 9 wherein the electrically conductive materialcomprises a conductive adhesive.
 11. The capacitor of claim 1 whereinthe anode termination is isolated from the capacitive element, otherthan by the external conduction connection, by plastic material.
 12. Thecapacitor of claim 11 wherein the plastic material comprises an epoxyadhesive.
 13. The capacitor of claim 12 further comprising an insulativelayer between the epoxy adhesive and the anode termination.
 14. Thecapacitor of claim 1 wherein the capacitive element comprises a solidbody.
 15. The capacitor of claim 14 wherein the solid body is a pellet.16. The capacitor of claim 15 wherein the pellet comprises tantalum,niobium, or niobium oxide.
 17. The capacitor of claim 15 wherein theanode comprises the pellet and a wire having a portion embedded in orwelded to the pellet and a portion outside of the pellet, and adielectric layer formed by oxidation of anode material, and the cathodecomprises an electrolyte layer on the exterior of the pellet.
 18. Thecapacitor of claim 17 wherein the portion of the wire outside the pelletis exposed at the surface of the case at which the external conductivepath is positioned.
 19. The capacitor of claim 18 wherein the surface ofthe case at which the external conductive path is positioned isgenerally in a first plane.
 20. The capacitor of claim 19 wherein theanode and cathode terminations are exposed externally of the case at ornear a second plane.
 21. The capacitor of claim 20 wherein the first andsecond planes are generally orthogonal.
 22. The capacitor of claim 1further comprising minimizing volume of the case around the capacitiveelement relative to the volume of the capacitive element.
 23. Thecapacitor of claim 22 wherein volume of the case is minimizing byminimizing wall thickness of the case by high precision molding andsingulation of the case.
 24. An electrical circuit board comprising: a)an electrical circuit board; b) an electrical circuit on the circuitboard including at least one surface mount capacitor; c) the surfacemount capacitor comprising a case of encapsulating material, acapacitive element inside the case including an anode and a cathode, aportion of the anode being exposed, an electrically conductive planarsubstrate comprising anode and cathode external terminations havingsurface mount portions outside and on one side of the case and to whichthe capacitive element is mounted, an external conductive connectionoutside the case in operative electrical communication with thecapacitive element and the exposed portion of the anode termination, andan at least partially internal conductive path between the cathodetermination and the capacitive element.
 25. The circuit board of claim24 wherein the external conductive path allows an improvement involumetric efficiency by allowing a larger capacitive element in thecase than if the anode termination was electrically connected to thecapacitive element through the case.
 26. The circuit board of claim 24further comprising minimizing volume of the case around the capacitiveelement relative to the volume of the capacitive element.
 27. Thecircuit board of claim 26 wherein volume of the case is minimizing byminimizing wall thickness of the case by high precision molding andsingulation of the case.
 28. The circuit board of claim 24 furthercomprising a plurality of said capacitors.
 29. The circuit board ofclaim 24 wherein the capacitive element comprises a solid pellet anodebody, an embedded or welded wire partially in the anode body, adielectric layer formed by oxidation of the anode body, and anelectrolyte layer over the dielectric layer.
 30. An electrical orelectronic device comprising: a) a housing and a user interface; b) anelectrical circuit board in the housing including at least one surfacemount capacitor; c) the surface mount capacitor comprising a case ofencapsulating material, a capacitive element inside the case includingan anode and a cathode, a portion of the anode being exposed, anelectrically conductive planar substrate comprising anode and cathodeexternal terminations having surface mount portions outside and on oneside of the case and to which the capacitive element is mounted, an atleast partially external conductive connection outside the case inoperative electrical communication with the capacitive element and theexposed portion of the anode termination, and an at least partiallyinternal conductive path between the cathode termination and thecapacitative element.
 31. The device of claim 30 wherein the externalconductive path allows an improvement in volumetric efficiency byallowing a larger capacitive element in the case than if the anodetermination was electrically connected to the capacitive element throughthe case.
 32. The device of claim 30 further comprising minimizingvolume of the case around the capacitive element relative to the volumeof the capacitive element.
 33. The device of claim 32 wherein volume ofthe case is minimizing by minimizing wall thickness of the case by highprecision molding and singulation of the case.
 34. The device of claim30 further comprising a plurality of said capacitors.
 35. The device ofclaim 30 wherein the capacitive element comprises a solid pellet anodebody, an embedded or welded wire in the anode body, a dielectric layerformed by oxidation of the anode body, and an electrolyte layer over thedielectric layer.
 36. The device of claim 30 wherein the devicecomprises a hand-held radio frequency communications device.
 37. Thedevice of claim 30 wherein the device comprises a medical instrument.38. The device of claim 30 wherein the device comprises amicroprocessor.
 39. A surface mount capacitor comprising: a) acapacitive element including an anode and a cathode; b) an encapsulationmaterial forming a case around the capacitive element except for anexposed portion of the anode; c) an electrically conductive planarsubstrate comprising anode and/or cathode terminations having surfacemounting portions on a single exterior side of the case and to which thecapacitive element is mounted; d) a conductive path between the exposedportion of the anode and the anode termination comprising an externalconductive connection on an external surface of the case wherein theanode termination is isolated from the capacitive element, other than bythe external conduction connection, by plastic material.
 40. Thecapacitor of claim 39 wherein the plastic material comprises an epoxyadhesive.
 41. The capacitor of claim 40 further comprising an insulativelayer between the epoxy adhesive and the anode termination.